Password/Login/Access

Is it possible to access the computer and data, having physical access and not knowing any passwords? Yes, it is.

Is it possible he already setup a master password he can use at any time? Yes, it is.

Can you, us, or anyone else tell if he already has the specific knowledge to do any of this, or is able to find it by googling the web? No, we can't.

1. Tell the flatmate to leave your stuff alone.
2. Get a safe or lockbox and keep your computer locked up while away from it.
3. Replace the flatmate.

Seriously, if he won't leave your stuff alone after you tell him to, what were you going to do anyway?

 

1. Set a firmware password. http://support.apple.com/kb/ht1352
(Note: be careful and never forget the password.) He wont be able to boot into the OS without knowing the firmware password or the login password if this is done.

2. Encrypt parts of your hard drive you don't want your flatmate seeing. You can do this by creating one or more encrypted .DMG's with Disk Utility and stuffing them with various files you want to keep to yourself. You can also mess around with an application called TrueCrypt. Again, be careful and know what you're doing before you start any major encryption.
It's worth noting that Lion will have full disk encryption, so that should keep Ubuntu flash drive users from snooping in your files.

 

The firmware password on a Mac is not the equivalent of a power-on password on a PC. A firmware password will prevent someone without it from changing the startup disk, booting to an install DVD, or resetting the PRAM. But the computer will still boot into the OS with one present and configured.

 

I know that. But assuming the intruder does not know the login password he would then try to boot from a CD, go into single user mode and make himself a new admin account, and so on. I was implying that wouldn't be possible with a firmware password.

I was merely listing things he should do. Perhaps I should have been more clear.

Derp.